BETHESDA, Md. (WUSA9) -- A parking deck collapse at Montgomery Mall left one person dead and another critically injured on Thursday. Officials expect a long investigation as they try to figure out exactly what happened.

Thursday afternoon, the Cabin John Park Volunteer Fire Department tweeted out that its units responded to Westfield Montgomery Mall "for major structure collapse." Later, Montgomery County Fire officials said they got a call at 1:47 p.m. at the location at 7125 Democracy Blvd. They told us a key section of the parking deck collapsed and they were trying to rescue two adults.

The collapse occurred between the second and third floors of the parking garage. A massive portion of a deck fell, trapping two men underneath a 55,000-pound slab of concrete and steel.

The two men were construction workers (the parking garage was not open to the public due to construction). One worker died but the second worker was trapped for about four hours before he was freed and flown to a hospital.

A team of surgeons from Baltimore Shock Trauma flew in to treat the man on the scene. We're told one of the surgeons actually was within feet of the victim at the scene, calming him down throughout the whole process as crews worked to free him. We're told the injuries were described as serious. Remarkably, that construction worker was alert and talking when he was finally rescued.

More than 100 people worked on the rescue, says Assistant Chief Scott Graham of Montgomery County Fire and Rescue.

The contractor Whiting Turner of Baltimore County was working on the parking garage at one point but we're uncertain if Whiting Turner was working on this particular phase of the project or if they had contracted it out. Of course, the county is pulling all the permits to try to get some answers.

The mall remained open during the collapse and Friday, the Macy's nearby remains open.

A parking garage collapse under construction in Rockville, Md. in 2002 killed one worker.